1. Field of the Invention
The present invention relates to a non-reciprocal circuit element which is for use in a high frequency band of about 0.5 to 3 GHz, for example, and more particularly, it relates to a high-frequency use non-reciprocal circuit element which is integrally provided with impedance-matching capacitance. The high-frequency use non-reciprocal circuit element according to the present invention may be a lumped parameter circulator or isolator, for example.
2. Description of the Background Art
Integration of high-frequency circuits has recently progressed in relation to mobile communication systems and the like, and hence miniaturization, cost reduction and improvement in reliability are required for a non-reciprocal circuit element which is employed for such an integrated circuit.
The non-reciprocal circuit element, such as a lumped parameter circulator or isolator, for example, comprises a plurality of central electrodes which are electrically insulated from each other by an insulator layer and arranged to intersect with each other, a high-frequency use magnetic body which is arranged on an intersectional portion of the central electrodes, and a permanent magnet for applying a dc magnetic field to the intersectional portion, with formation of impedance-matching capacitance, for example.
FIG. 6 is a perspective view for illustrating an exemplary step of assembling a conventional high-frequency use non-reciprocal circuit element. In order to assemble the high-frequency use non-reciprocal circuit element, a central electrode 124a of metal foil such as Cu foil, for example, is first arranged on a discoidal high-frequency use magnetic body 123a.
The central electrode 124a radially extends along an upper surface of the high-frequency use magnetic body 123a through its center, to reach side surfaces of the magnetic body 123a.
Then, an insulating film 125a of an insulating material is arranged on the central electrode 124a, and another central electrode 124b is arranged thereon to intersect with the central electrode 124a. Further, another insulating film 125b, still another central electrode 124c and still another insulating film 125c are successively stacked on the central electrode 124b, and a high-frequency use magnetic body 123b is stacked on the uppermost portion.
The high-frequency use non-reciprocal circuit element which is assembled in the aforementioned manner is combined with a permanent magnet, yokes holding the permanent magnet and other conventional components to form a circulator or an isolator, as shown in FIG. 7 in an exploded perspective view.
Referring to FIG. 7, a rectangular substrate 131 of an insulating material such as alumina is provided in its center with a through hole 131a for receiving the aforementioned high-frequency use non-reciprocal circuit element. Electrodes 132 for deriving capacitance are formed on an upper surface of the substrate 131 by printing conductive films.
On the other hand, an earth electrode is formed on a lower surface of the substrate 131, to be opposed to the capacitance deriving electrodes 132 through the substrate 131. An earth plate 133 illustrated in a lower portion is bonded to this earth electrode by soldering, to be integrated with the substrate 131. The earth plate 133 is formed by a metal plate, and provided with a through hole 133a in its center and uprights 133b in portions facing the through hole 133a. When the substrate 131 and the earth plate 133 are bonded to each other as described above, the uprights 133b upwardly project from the through hole 131a of the substrate 131.
As clearly understood from FIG. 8 showing a principal part of the assembly as formed, the uprights 133b are soldered to first ends of the central electrodes 124a to 124c of the aforementioned high-frequency use non-reciprocal circuit element respectively by soldering or the like. Referring to FIG. 8, the insulating films 125a to 125c are omitted, while numeral 137 denotes the earth electrode which is formed on the lower surface of the substrate 131. The capacitance deriving electrodes 132, the substrate 131 and the earth electrode 137 provided on the back surface of the substrate 131 form impedance-matching capacitance.
On the other hand, second ends of the central electrodes 124a to 124c of the high-frequency non-reciprocal circuit element are electrically connected to the capacitance deriving electrodes 132 which are formed on the upper surface of the substrate 131 respectively, as understood from the central electrode 124c typically shown in FIG. 8, for example.
Referring again to FIG. 7, the substrate 131 and the earth plate 133 are stacked with each other and the high-frequency use non-reciprocal circuit element is integrated into the through holes 131a and 133b, and the laminate as formed is held by yokes 134 and 135 from upper and lower portions, thereby forming a high-frequency use non-reciprocal circuit device. A permanent magnet 136 is fixed to a lower surface of the yoke 134. The yokes 134 and 135, which are made of a metal, have pairs of opposite ends which are bent toward each other, to be fixed to each other through the bent portions by soldering or mechanical engagement. Therefore, the yokes 134 and 135 and the permanent magnet 136 form a closed magnetic circuit for applying a dc magnetic field to the central electrodes 124a to 124c.
As described above, the conventional high-frequency use non-reciprocal circuit element requires a complicated manual operation for assembling the structure shown in FIG. 8, as well as soldering and a complicated manual operation for connecting the permanent magnet for applying a dc magnetic field and the earth electrode.
In the conventional high-frequency use non-reciprocal circuit element, as hereinabove described, insulating resin films or resin tapes are interposed between the central electrodes, or insulating substrates having central electrodes printed thereon are pasted to each other, in order to electrically insulate the central electrodes from each other. Further, the aforementioned insulating films and the insulating substrate are generally successively assembled by a manual operation. In addition, it is generally necessary to add capacitance to the high-frequency use non-reciprocal circuit element for impedance matching. Such capacitance for an impedance-matching circuit is added by connecting a separately prepared capacitor, or by forming a capacitor through an insulating substrate and combining the same with the high-frequency use non-reciprocal circuit as described above, also by a manual operation.
With progress in miniaturization and generalization of the high-frequency use non-reciprocal circuit element, however, its dimensions are now being reduced to millimeters. Thus, it is extremely difficult to manually assemble such a small element, such that imperfect assembling is frequently caused by misregistration between central electrodes and capacitance for an impedance-matching circuit, leading to reduction in reliability.
In the conventional high-frequency use non-reciprocal circuit element, as described above, it is necessary to manually assemble not only the principal part which is provided with a plurality of central electrodes and a high-frequency use magnetic body but also a capacitor for forming additional capacitance for impedance matching through complicated manual operations, and the number of components is greatly increased, leading to a great increase in cost.